The
Critics Say: “CO2 lags behind temperature
by centuries in the glacial-interglacial cycles, so clearly CO2
does not cause temperatures to rise, temperatures cause CO2
to rise.”

Just a bit of
illogic here. But don't think the simplicity of the explaination
means it will sway any of the die-hards.

Answer:A close examination of the CH4, CO2
and temperature fuctuations recorded in the Antarctic
ice core records
does in fact reveal that yes, the temperature moved first in what is,
when viewed coarsely, a very
tight correlation.
But what is not correct is to say the temperature rose and then 800
years later the CO2 rose. These warming periods lasted for
5000 to 10000 years (the coolings lasted ~100kyrs) so for the
majority of that time (~90%) temperature and CO2 rose
together. This means that this wonderful archive of climatological
evidence clearly allows for CO2 acting as a cause while
also revealing it can be an effect.

The current understanding
of those cycles is that changes in orbital parameters (Milankovich
and
other
cycles)
caused greater amounts of summer sunlight in the northern hemisphere.
This is a very small forcing. But it caused ice to retreat in the
north which changed the albedo increasing the warmth in a feedback
effect. Some ~800 years after this process started, CO2
concentrations in the atmosphere began to rise and this also
amplified the warming trend even further as another feedback
mechanism.

You can also go here:
http://www.realclimate.org/index.php?p=13
for a discussion by climate scientists of exactly this question but
with greater technical detail and full references to the scientific
literature.

So, CO2 did not trigger
past warmings, but it did contribute
to them, and according to climate theory and model experiments,
Greenhouse Gas forcing was the largest factor in the ultimate
change.One thing that this says for the future is that we may well
see additional natural CO2 come out of the woodwork as
whatever process that took place repeatedly over the last 650K yrs
begins to play out again. The likely candidates are outgassing from
warming ocean waters, carbon from warming soils and methane from
melting
permafrost.
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